U.S. patent number 7,719,284 [Application Number 11/285,319] was granted by the patent office on 2010-05-18 for apparatus for measuring voltage.
This patent grant is currently assigned to Honda Motor Co., Ltd., Keihin Corporation. Invention is credited to Toshiaki Ariyoshi, Masanori Kawamoto, Yuji Minoda, Yoshikazu Nomoto, Takayuki Ohta.
United States Patent |
7,719,284 |
Ohta , et al. |
May 18, 2010 |
Apparatus for measuring voltage
Abstract
An apparatus measures a voltage of a cell while scanning a group
of cells in a cell stack, in which a plurality of cells is
electrically connected in series. The apparatus has a first
switching device and a voltage detecting device. The first
switching device is connected in series with a signal line carrying
a voltage of a cell. The voltage detecting device detects the
voltage of the cell, which is electrically connected with signal
lines carrying voltages of cells belonging to a group. When the
first switching device is electrically connected with a connecting
point between two successive groups of cells, the first switching
device is shared by the two groups.
Inventors: |
Ohta; Takayuki (Tochigi,
JP), Kawamoto; Masanori (Tochigi, JP),
Minoda; Yuji (Saitama, JP), Ariyoshi; Toshiaki
(Saitama, JP), Nomoto; Yoshikazu (Saitama,
JP) |
Assignee: |
Keihin Corporation (Tokyo,
JP)
Honda Motor Co., Ltd. (Tokyo, JP)
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Family
ID: |
36594847 |
Appl.
No.: |
11/285,319 |
Filed: |
November 23, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060132139 A1 |
Jun 22, 2006 |
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Foreign Application Priority Data
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Nov 30, 2004 [JP] |
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2004-346959 |
Nov 30, 2004 [JP] |
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2004-347874 |
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Current U.S.
Class: |
324/434; 324/426;
320/116 |
Current CPC
Class: |
G01R
31/396 (20190101); H02J 7/0021 (20130101); G01R
31/389 (20190101) |
Current International
Class: |
G01N
27/416 (20060101) |
Field of
Search: |
;320/116
;324/426,434 |
References Cited
[Referenced By]
U.S. Patent Documents
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5712568 |
January 1998 |
Flohr et al. |
6639408 |
October 2003 |
Yudahira et al. |
6639409 |
October 2003 |
Morimoto et al. |
6677758 |
January 2004 |
Maki et al. |
6803766 |
October 2004 |
Kobayashi et al. |
7078908 |
July 2006 |
Fujita et al. |
|
Foreign Patent Documents
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11-237455 |
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Aug 1999 |
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JP |
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11-339828 |
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Dec 1999 |
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JP |
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2000-193694 |
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Jul 2000 |
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JP |
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2002-139522 |
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May 2002 |
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JP |
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2002-156392 |
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May 2002 |
|
JP |
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2002-350472 |
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Dec 2002 |
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JP |
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2004-085208 |
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Mar 2004 |
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JP |
|
Primary Examiner: Tso; Edward
Assistant Examiner: Ramadan; Ramy
Attorney, Agent or Firm: Kratz, Quintos & Hanson,
LLP
Claims
What is claimed is:
1. An apparatus for measuring a voltage of a cell while scanning a
group of cells in a cell stack having a plurality of cells
electrically connected in series, the apparatus comprising: a first
switching device that is connected in series with a signal line
carrying a voltage of a cell; a voltage detecting device for
detecting the voltage of the cell, the voltage detecting device
being electrically connected with signal lines that carry voltage
of cells belonging to a group, wherein when the first switching
device is electrically connected with an interface between two
successive groups of cells, the first switching device is shared by
the two groups; and a second switching device for selecting a line
to be grounded from two signal lines which carry voltages of cells
lying in interfaces on both sides of the group of cells, wherein
the line to be grounded is alternately selected from two signal
lines and grounded depending on whether an oddly or evenly numbered
group is scanned, wherein the voltage detecting device detects the
voltage of the cell when either of two lines is grounded, wherein
the voltage detecting device comprises a differential amplifier,
and wherein when the oddly numbered group is scanned, one of two
signal lines which is a low voltage side in the oddly numbered
group is selected to be grounded, and the differential amplifier
adds a first offset voltage to an input voltage thereof, and when
the evenly numbered group is scanned, one of two signal lines which
is a high voltage side in the evenly numbered group is selected to
be grounded, and the differential amplifier adds a second offset
voltage higher than the first voltage to the input voltage
thereof.
2. An apparatus according to claim 1, wherein an offset voltage is
imposed on an input voltage of the voltage detecting device and the
offset voltage is adjusted to be higher for a group of cells which
is electrically connected with the voltage detecting device in such
a manner that a relatively higher side of the group in terms of
voltage is grounded.
3. An apparatus according to claim 1, wherein the first switching
device is a PhotoMOS relay having a withstand voltage which is
higher than a voltage of the cell stack.
4. An apparatus according to claim 1, wherein every time one of the
two signal lines is grounded by switching provided by the second
switching device, the voltage detecting device detects a voltage of
a cell in a constant polarity.
5. An apparatus according to claim 1, wherein the two signal lines
are alternately grounded, depending on the group of cells which is
oddly or evenly numbered with respect to an initial group of cells,
for which measurement is first carried out.
6. An apparatus according to claim 1, wherein the second switching
device is a PhotoMOS relay having a withstand voltage which is
higher than a voltage of the cell stack.
7. An apparatus according to claim 1, wherein the cell stack is a
fuel cell stack.
8. An apparatus according to claim 1, wherein the second switching
device is common to all cells.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring
voltage, and more particularly to an apparatus for measuring
voltage of a cell while scanning a group of cells in a cell stack
such as a fuel cell stack in which a plurality of cells is
electrically connected in series.
A fuel cell is a type of battery which generates electromotive
force by electrochemical reaction between hydrogen contained in a
fuel gas as a main substance and oxygen. As a cell voltage of the
fuel cell only reaches as high as 1 volt, some hundreds of cells
are in general electrically connected in series to form a fuel cell
stack, which provides a high voltage, 260 volts, for example. If
power generation is continued while one cell generates an extremely
low voltage, 0.5 volts for example, it may result in damage of the
fuel cell stack due to a drop in its aggregate output voltage,
which is caused by corrosion occurring in the failed cell. It is
typical that measurement and monitoring of a voltage of cell is
carried out during operation of a fuel cell stack by scanning cells
one by one or a group of cells group by group. In this way,
continuous measurement and monitoring of a cell voltage provides
prompt notification of occurrence of an abnormal cell, because when
a cell or a plurality of cells suffers damage, there is a
remarkable drop in voltage. Accordingly, it is possible to
immediately stop operation of the fuel cell stack so as to prevent
development of damage which results from delay in sensing an
occurrence of abnormal operation.
An example of measurement of voltage for an individual cell is
disclosed in patent document 1, which uses a terminal shaped like a
projection provided for a separator between successive cells.
Because a hole is no more required of an end surface of the
separator by introduction of the terminal, a socket of a lead wire
can be connected with the terminal even if the separator gets
thinner. Accordingly, it is possible to measure a voltage for the
individual cell even if a fuel cell decreases in dimension.
Various techniques associated with measurement of cell voltage for
a fuel cell have been reported. FIG. 5 is a diagram showing a
conventional apparatus for measuring voltage. As shown in FIG. 5, a
voltage of an individual cell is measured and monitored in the
following manner. Cells contained in a fuel cell are divided into a
plurality of groups. For example, when switches S31, S32, S33 and
S34 belonging to a first group are simultaneously turned on,
individual voltages of cells C31, C32 and C33 belonging to the
first group are detected by differential amplifiers D31, D32 and
D33 of a detecting circuit 30. The voltages are sent to an A/D
converter of a central processing unit (CPU) (not shown), where
measurement and monitoring are carried out. Subsequently, when the
switches S31, S32, S33 and S34 of the first group are
simultaneously turned off and switches S35, S36, S37 and S38
belonging to a second group are simultaneously turned on,
individual voltages of cells C34, C35 and C36 belonging to the
second group are detected by the differential amplifiers D31, D32
and D33, and measured and monitored by the CPU. In this way, it is
possible to measure a voltage of each cell in the fuel cell by
scanning groups one by one while switches of the groups are turned
on and off one after another.
FIG. 6 is a diagram illustrating a polarity of measured voltage for
each cell in the detecting circuit shown in FIG. 5. When groups of
cells are scanned group by group as described above, voltages
imposed on the differential amplifiers D31, D32 and D33 have a
constant polarity irrespective of groups. This will allow use of a
single power supply, which for example is a one-way power supply
having a ground and a positive power source, for each of the
differential amplifiers D31, D32 and D33. In this way, the
differential amplifiers D31, D32 and D33 can be simply configured.
In this connection, filters F31, F32 and F33 disposed in the
detecting circuit 30 are elements for removing noise. Buffers B31,
B32 and B33 are elements for shaping a wave form of detected
voltage.
A technique related to an apparatus for measuring voltage using a
flying capacitor is disclosed in patent document 2. The technique
is applied to a fuel cell stack in which many cells are
electrically connected in series. A capacitor is connected in
parallel with each of the cells, and a group is arranged so as to
include five cells, for example. Measurement of voltage is carried
out by detecting a voltage imposed on a capacitor corresponding to
a cell while a switch corresponding to this cell is turned on. By
repeating this measurement with switching, it is possible to
measure voltages for all the cells of the group. The measurement is
carried out for groups one after another so as to complete
measurement for all the cells in the fuel cell stack. This
technique results in a simplified configuration of circuit. In
addition, a technique is disclosed in patent document 3, which
measures voltages of individual cells one by one using a plurality
of switches in a fuel cell stack, in which a plurality of cells is
electrically connected to each other in series. This technique
brings about measurement of a voltage of an individual cell with
high precision, which does not require a complicated setup. Patent
document 1: Japanese Published Patent Application 11-339828 Patent
document 2: Japanese Published Patent Application 2002-156392
(paragraphs 0051-0058, and FIG. 1) Patent document 3: Japanese
Published Patent Application 11-237455 (paragraphs 0018- 0024, FIG.
1 and FIG. 2)
Because a large number of cells are electrically connected to each
other in series, the detecting circuit shown in FIG. 5 requires
more pieces of switches than number of cells so as to measure a
voltage for an individual cell. Specifically speaking, a cell lying
in an interface between two successive groups requires two pieces
of switches so as to turn off one signal line of a previous group
and to turn on the other line of a next group. For example, the
cell C34 lying in one interface between a first group and a second
group requires the switches S34 and S35. Similarly, the cell C36
lying in the other interface of the second group and a third group
requires the switches S38 and S39. It is deduced that switches more
than 181 pieces, namely 181+180/3-1=240 pieces, are necessary in
case of a fuel cell stack having 180 cells electrically connected
to each other in series, when a group is arranged so as to include
three cells. Because PhotoMOS relays having high withstand voltage
are in general selected for these switches, the more the number of
switches increases, the more expensive material cost will be. In
this connection, it may be possible to anticipate some decrease in
total number of switches if number of cells belonging to a group is
increased. The reason for this is that number of switches
decreases, which lie in an interface between successive groups.
However, an increase in the number of cells belonging to a group
induces an increase in number of filters, buffers and differential
amplifiers in a detecting circuit 30, resulting in an increase in
material cost of an apparatus for measuring voltage as a whole.
Although the apparatus for detecting voltage disclosed in patent
document 2 simplifies a setup of a circuit made of switches, it
additionally requires a capacitor on which a voltage of a cell is
imposed, resulting in a cost increase. In addition, the circuit for
detecting voltage for a cell stack disclosed in patent document 3
has a drawback that a setup of circuit for switching devices turns
complex.
SUMMARY OF THE INVENTION
In view of the drawbacks described above, the present invention
seeks to provide an apparatus for measuring voltage, which is able
to provide efficient measurement with a simple setup of circuit due
to a decrease in the number of switches, in carrying out
simultaneous measurement of voltage for a plurality of cells.
It is an aspect of the present invention to provide an apparatus
for measuring a voltage of a cell while scanning a group of cells
in a cell stack in which a plurality of cells is electrically
connected in series. The apparatus comprises a first switching
device and a voltage detecting device. The first switching device
is connected in series with a signal line carrying a voltage of a
cell. The voltage detecting device detects the voltage of the cell,
which is electrically connected with signal lines carrying voltages
of cells belonging to a group. When the first switching device is
electrically connected with a connecting point between two
successive groups of cells, the first switching device is shared by
the two groups.
It is another aspect of the present invention to provide an
apparatus, which further comprises a second switching device. The
second switching device selects a line to be grounded from two
signal lines, which carry voltages of cells lying in interfaces on
both sides of the group of cells. Every time one of the two signal
lines is grounded by switching provided by the second switching
device, the voltage detecting device detects a voltage of a cell in
a constant polarity.
The apparatus described above is able to decrease total number of
switching devices to a minimum. Introduction of sharing of a
switching device causes reversal of polarity, between a positive
and a negative polarity, when measurement is transferred from a
group to an adjacent group. The apparatus according to the present
invention, which switches signal lines so as to connect to the
ground for a group of cells to be measured, provides a constant
polarity of a cell voltage to the voltage detecting device. In this
way, it is possible to operate the voltage detecting device by use
of a single power supply.
As a result, a device which can be operated by a single power
supply, such as a differential amplifier, for the voltage detecting
device, which contributes to a large amount of decrease in material
costs of an apparatus for measuring voltage. As signal lines lying
both ends of a group of cells are alternately switched so as to be
connected to the ground each time a polarity of the group reverses,
number of cells which can be scanned at one time will be doubled.
Because scanning is carried out more rapidly for multi channels, it
is possible to measure voltage for cells more rapidly, which are
electrically connected to each other in series to form a group.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram showing a main portion of an apparatus
for measuring voltage, which introduces sharing of a switch which
lies in an interface between successive groups.
FIG. 2 is a schematic diagram illustrating a polarity of detected
voltage of a cell in the detecting circuit shown in FIG. 1.
FIG. 3 is a circuit diagram showing an apparatus for measuring
voltages according to the present invention.
FIG. 4 is a circuit diagram showing an example of an apparatus for
measuring voltage according to the present invention, assuming that
a group includes four cells.
FIG. 5 is a diagram showing a conventional apparatus for measuring
voltage.
FIG. 6 is a diagram illustrating a polarity of measured voltage for
each cell in the detecting circuit shown in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description is given of an embodiment of an apparatus for measuring
voltage according to the present invention with reference to
drawings. Measurement of cell voltage for a fuel cell, in which a
large number of cells are electrically connected to each other in
series, will be efficiently carried out in the following manner.
The cells are divided into groups, each of which is arranged so as
to include certain plural number of cells. Measurement is
simultaneously carried out for individual cells belonging to a
group. Another measurement is carried out by scanning a subsequent
group of cells. Scanning groups one by one can be carried out by
simultaneously turning on or off switches belonging to a group,
each of which is provided for an input terminal (signal line) of
each cell for measuring voltage. Separate switches are not provided
for a signal line lying in an interface between two successive
groups, but a common switch is shared by the groups. In other
words, although scanning is transferred from one group to a
subsequent group, the common switch is left turned on.
Description is given of the embodiment of the present invention
below, taking into account the setup described above which helps
reduce required number of switches.
Before describing an apparatus for measuring voltage according to
the present invention, description is first given of a circuit
which plays a background role in the invention.
Description is given of an example as shown in FIG. 1, in which
measurement is carried out for a voltage of an individual cell
while scanning is made for groups one by one, which is arranged so
as to include three cells for convenience sake. The example does
not limit the number of cells belonging to a group to three, but it
may be alternatively possible to select larger number of cells for
a group. It is natural that increasing the number of cells in a
group should result in a decrease in time required for completing
measurement for all the cells.
As shown in FIG. 1, in a detecting circuit 10 (voltage detecting
device), cells C1 to C9 are connected to each other in series,
which occupy a portion of a fuel cell in which a large number of
cells are connected to each other in series. These cells C1 to C9
are divided into groups: a first group of C1, C2 and C3, a second
group of C4, C5 and C6, and a third group of C7, C8 and C9. While
scanning is made for these groups one by one, measurement is
simultaneously carried out for cells belonging to a group. Switches
(switching devices) S1 to S10 are connected with signal lines,
which serve as terminals for measurement of voltage for the cells
C1 to C9, respectively. The switch C4 shared by the two groups is
provided for a signal line lying in an interface between the last
cell C3 of the first group and the first cell C4 of the second
group. Similarly, the shared switch C7 is provided for a signal
line lying in an interface between the last cell C6 of the second
group and the first cell C7 of the third group. A signal line of
negative polarity of the first cell C1 belonging to the first group
is connected to the ground GND. In this connection, it may be
possible to adopt FotoMOS relays, which can withstand a maximum
voltage resulting from cells connected in series in a fuel cell,
260 volts in case of 200 cells for example, for the switches S1 to
S10.
Signal lines for respective groups are connected with the detecting
circuit 10. The detecting circuit 10 includes filters F1, F2 and
F3, buffers B1, B2 and B3, differential amplifiers D1, D2 and D3
and a resister R.sub.o. The filters F1 to F3 remove noise which
occurs during turning on and off of the switches S1 to S3, or noise
induced by the signal lines. The buffers B1 to B3, which are
connected with the filters F1 to F3 respectively, shape unevenness
occurring in rising and falling waveforms. The differential
amplifiers D1 to D3, which receive negative and positive voltages
from the cells C1 to C9 so as to detect their voltages, sending the
detected voltages to the A/D converter of the CPU (not shown). The
resister Ro adjusts an offset voltage for each of the differential
amplifiers D1 to D3. In addition, there is a resister R.sub.L
between an output of each of the buffers B1 to B3 and a positive
input terminal of each of the differential amplifiers D1 to D3, so
that a signal level of the positive input terminal is adjusted.
Description is given of measurement of voltage for the cells C1 to
C9 with the detecting circuit 10 shown in FIG. 1. When the switches
S1 to S4 are simultaneously turned on, voltages of the cells C1 to
C3 belonging to the first group are simultaneously measured. More
specifically speaking, a potential of a negative polarity of the
cell C1, which is connected to the ground GND, enters a negative
input terminal of the differential amplifier D1. On the other hand,
a potential of a positive polarity of the cell C1 enters a positive
input terminal of the differential amplifier D1 via the filter F1
and the buffer B1. In this way, a voltage of the cell C1, which is
a difference in potential between the positive and negative
polarities of the cell C1, is generated, so that a signal
indicative of the voltage of the cell C1 comes out from an output
terminal of the differential amplifier D1.
Similarly, a potential of a negative polarity of the cell C2 enters
a negative input terminal of the differential amplifier D2 via the
filter F1 and the buffer B1. On the other hand, a potential of a
positive polarity of the cell C2 enters a positive input terminal
of the differential amplifier D2 via the filter F2 and the buffer
B2. In this way, a voltage of the cell C2, which is a difference in
potential between the positive and negative polarities of the cell
C2, is generated, so that a signal indicative of the voltage of the
cell C2 comes out from an output terminal of the differential
amplifier D2.
In the same manner as described above, a signal indicative of a
voltage of the cell C3 comes out from an output terminal of the
differential amplifier D3. The voltages, which the differential
amplifiers D1 to D3 have simultaneously measured for the cells C1
to C3 belonging to the group 1, are sent to the CPU (not shown).
Following combination of cells with differential amplifiers is
called forward measurement: the cell C1 is assigned to the
differential amplifier D1, the cell C2 to the differential
amplifier D2 and the cell C3 to the differential amplifier D3,
which are hereinafter referred to as C1 .fwdarw.D1, C2.fwdarw.D2
and C3.fwdarw.D3, respectively.
When the measurement for the cells C1 to C3 is completed and
another measurement for the cells C4 to C6 is started, the switches
S5 to S7 are simultaneously turned on after the switches S1 to S3
have been simultaneously turned off, leaving the switch S4 turned
on. It should be noted that the shared switch S4 connected with a
common signal line for the last cell C3 of the first group and the
first cell C4 of the second group is left turned on. Under
switching operation described above, the cells belonging to the
second group are measured in the following way: the cell C4 is
measured by the differential amplifier D3, the cell C5 by the
differential amplifier D2 and the cell C6 by the differential
amplifier D1. In this measurement of the second group, combination
of cells with differential amplifiers is reversed in comparison
with the first group. This combination, C4.fwdarw.D3, C5.fwdarw.D2
and C6 .fwdarw.D1, is hereinafter referred to as backward
measurement.
More detail description is given of measurement of voltage for the
cells C4 to C6 of the second group. When the measurement for the
cells C1 to C3 is completed, the switches S5 to S7 are
simultaneously turned on after the switches S1 to S3 have been
simultaneously turned off, leaving the switch S4 turned on. In this
way, another measurement for the cells C4 to C6 is initiated. A
potential of a negative polarity of the cell C4 enters the positive
input terminal of the differential amplifier D3 via the filter F3
and the buffer B3. On the other hand, a potential of a positive
polarity of the cell C4 enters the negative input terminal of the
differential amplifier D3 via the filter F2 and the buffer B2. In
this way, a voltage of the cell C4, which is a difference in
potential between the positive and negative polarities of the cell
C4, is generated, so that a signal indicative of the voltage of the
cell C4 comes out from the output terminal of the differential
amplifier D3.
Similarly, a potential of a negative polarity of the cell C5 enters
the positive input terminal of the differential amplifier D2 via
the filter F2 and the buffer B2. On the other hand, a potential of
a positive polarity of the cell C5 enters the negative input
terminal of the differential amplifier D2 via the filter F1 and the
buffer B1. In this way, a voltage of the cell C5, which is a
difference in potential between the positive and negative
polarities of the cell C5, is generated, so that a signal
indicative of the voltage of the cell C5 comes out from the output
terminal of the differential amplifier D2.
A potential of a negative polarity of the cell C6 enters the
positive input terminal of the differential amplifier D1 via the
filter F1 and the buffer B1. On the other hand, a potential of a
positive polarity of the cell C6, which is connected to the ground
GND, enters the negative input terminal of the differential
amplifier D1. In this way, a voltage of the cell C6, which is a
difference in potential between the positive and negative
polarities of the cell C6, is generated, so that a signal
indicative of the voltage of the cell C6 comes out from the output
terminal of the differential amplifier D1.
The voltages, which the differential amplifiers D1 to D3 have
simultaneously measured for the cells C4 to C6 belonging to the
second group, are sent to the CPU (not shown). In measurement of
the second group, backward measurement is carried out, in which the
cells and differential amplifiers are combined as follows:
C4.fwdarw.D3, C5.fwdarw.D2 and C6.fwdarw.D1.
When the measurement for the cells C4 to C6 is completed, the
switches S8 to S10 are simultaneously turned on after the switches
S4 to S6 have been simultaneously turned off, leaving the switch S7
turned on. In this way, another measurement for the cells C7 to C9
is initiated. In measurement of the third group, forward
measurement in the same manner as that of the first group is
carried out, in which the cells and differential amplifiers are
combined as follows: C7.fwdarw.D1, C8.fwdarw.D2 and C9.fwdarw.D3.
The voltages, which the differential amplifiers D1 to D3 have
simultaneously measured for the cells C7 to C9 belonging to the
third group, are sent to the CPU (not shown).
The apparatus for measuring voltage according to the present
invention described above, which introduces sharing of a switch
lying in an interface of successive groups, allows small number of
switches in comparison with a conventional apparatus shown in FIG.
5. Suppose 180 cells are electrically connected to each other in
series and a group is arranged so as to include 3 cells. In this
case, the conventional apparatus requires 240 pieces of switches.
In contrast, the apparatus for measuring voltage according to the
present invention shown in FIG. 1 is able to reduce the number of
switches to 181 pieces, which means it is possible to reduce by 59
pieces in comparison with the conventional apparatus. To put it
differently, this reduction is comparable to number of groups.
If a voltage imposed on the A/D converter of the CPU falls
negative, to which output signals (detected voltages) of the
differential amplifiers D1 to D3 are sent, in measurement carried
out by the detecting circuit 10 shown in FIG. 1, stricter
requirements are requested to apply to the A/D converter. It is
possible to cope with the difficulty by introducing selection of
offset voltage. Suppose electromotive force of a cell ranges zero
to 1.3 volts, for example, as is typically the case with a fuel
cell. If an offset voltage of +1 volt for forward measurement and
an offset voltage of +5 volts for backward measurement are selected
for the detecting circuit 10 shown in FIG. 1, voltages imposed on
the A/D converter fall within a range of +1 to +5 volts, which
relaxes requirements applied to the A/D converter.
Next, description is given of a polarity of voltage of a cell,
which is imposed group by group on the differential amplifiers D1
to D3. When measurement is carried out one after another by turning
on and off switches in the apparatus for measuring voltage shown in
FIG. 1, detected voltages of cells enter group by group the
differential amplifiers D1 to D3 with polarities as shown in FIG.
2. It is known from FIG. 2 that in an oddly numbered group, the
first group for example, voltages of cells (C1 to C3) are forwardly
imposed on the differential amplifiers D1 to D3 while a negative
pole of the cell C1 with the lowest potential is connected to the
ground GND. In contrast, in an evenly numbered group, the second
group for example, voltages of cells (C4 to C6) are backwardly
imposed on the differential amplifiers D1 to D3 while a positive
pole of the cell C6 with the highest potential is connected to the
ground GND.
As shown in FIG. 2, a polarity of voltage imposed on the
differential amplifiers D1 to D3 in measurement of an oddly
numbered group is opposite to that in an evenly numbered group.
Accordingly, it is necessary to provide a source voltage, which is
imposed on the respective differential amplifiers D1 to D3, so that
its polarities are opposite to each other between the oddly and
evenly numbered groups at measurement. For example, the
differential amplifiers D1 to D3 require a power source of zero to
plus 5 volts in measurement of an oddly numbered group, but they
require a power source of minus 5 to zero volts in measurement of
an evenly numbered group. The differential amplifiers D1 to D3
require a power source having both positive and negative polarities
(bipolar power source) so as to carry out measurement for all the
cells in a fuel cell. This results not only in complication of
power source circuit (not shown) in the detecting circuit 10 shown
in FIG. 1, but also in necessity of differential amplifiers
compatible with a bipolar power source, which are more expensive
than those compatible with a single power source.
Furthermore, because a power source voltage for the differential
amplifiers D1 to D3 is defined in their specification, number of
channels (number of cells) at one scanning is automatically
determined so as to satisfy the power source voltage in the
detecting circuit shown in FIG. 1. Suppose a maximum rated voltage
for the differential amplifiers D1 to D3 is 20 volts and a cell
voltage of 3 volts for a pair of cells. In this case, number of
cells which can be measured at a time of scanning turns out to be
three cells (20V/2/3V.apprxeq.3 ). Because the number of cells
which can be scanned is not freely selected but restricted to be
not more than three, it may not be possible to increase number of
cells belonging to a group so as to shorten time required for
measurement. When a signal line shared by successive groups in the
apparatus for measuring voltage shown in FIG. 1, which is connected
to the ground, fails due to a malfunction, disconnection for
example, a problem shows up. If a signal line for the switch S4
shared by the first and second groups fails due to disconnection,
for example, it will end up with losing measurement of voltage for
the cells C1 to C3 of the first group and the cells C4 to C6 of the
second group.
The apparatus for measuring voltage according to the present
invention not only allows a reduction in the number of switches as
shown in FIG. 1, but also introduces a switch, which provides
switching for selection of a signal line to be connected to the
ground GND. The switch carries out the switching so that a signal
carrying a negative voltage of a cell, which enters a differential
amplifier as a measurement reference for the detecting circuit 10,
is arranged so as to be a reference potential (ground potential)
irrespective of groups to be scanned. Because the differential
amplifier detects a constant polarity of cell voltage in
measurement of any group, it is possible to adopt a differential
amplifier compatible with a single power source. Therefore, it is
possible to achieve a further decrease in cost for the apparatus
for measuring voltage as a whole. Also the introduction of the
switch prevents losing measurement of voltage for all the cells
belonging to the two groups at a failure due to disconnection of a
signal line shared by the groups, thereby minimizing the
failure.
Switches S11 and S12 (switching devices), which are for selecting a
signal line to be connected to the ground GND, are added to a
detecting circuit (voltage detecting device) 10a shown in FIG. 3 in
comparison with the detecting circuit shown in FIG. 1. Description
is not repeated for other elements which are the same as those
shown in FIG. 1. In this connection, it may be alternatively
possible to adopt FotoMOS relays, which can withstand a maximum
voltage resulting from cells connected in series in a fuel cell,
260 volts in case of 200 cells for example, for the switches S11
and S12 like the switches S1 to S10.
As shown in FIG. 3, two lines are added. One line connects a signal
line (signal line of a negative pole of the cell C1 belonging to
the first group), which enters a negative input terminal of the
differential amplifier D1, to the ground GND via the switch S11.
The other line connects a signal line (signal line shared by a
positive pole of the cell C3 belonging to the first group and a
negative pole of the cell C4 belonging to the second group), which
enters a positive input terminal of the differential amplifier D3,
to the ground GND via the switch S12.
In a setup of circuit described above, the switches 11 and 12 are
alternately turned on and off each time measurement is transferred
from one group to another so that one of the two signal lines
described above is alternately connected to the ground GND. In
other words, a reference potential (ground potential) of a cell
voltage is alternately connected with one of the negative input
terminal of the differential amplifier D1 and the positive input
terminal of the differential amplifier D3 according to a group to
be measured.
Detailed description is further given as follows. Although order of
cell voltages entering the differential amplifiers D1 to D3 vary
between the forward and backward measurement, a negative potential
of a differential amplifier serving as a reference is always
connected to the ground GND by switching. The forward measurement
represents connection between cells and differential amplifiers as
follows: C1.fwdarw.D1, C2.fwdarw.D2 and C3.fwdarw.D3. On the other
hand, the backward measurement as follows: C4.fwdarw.D3,
C5.fwdarw.D2 and C6 .fwdarw.D1. Because the ground GND of the
differential amplifiers D1 to D3 is arranged depending on forward
or backward measurement, it is possible to adopt a single power
source, in which a single sign of potential is provided with
respect to a reference potential (ground potential), as a power
supply for the differential amplifiers D1 to D3.
Further detailed description is given of the detecting circuit 10a
shown in FIG. 3. When measurement is carried out for the cells C1
to C3 of the first group, the switch S11 as well as the switches S1
to S4 are turned on. In this way, forward measurement is carried
out, in which combination of the cells and the differential
amplifiers are as follows: C1.fwdarw.D1, C2.fwdarw.D2 and
C3.fwdarw.D3. Because a ground potential (reference potential) is
allocated to the negative input terminal of the differential
amplifiers D1 by the switch S11, all the differential amplifiers D1
to D3 are able to work with a single power source.
When the measurement of the cells C1 to C3 has been completed and
another measurement of the cells C4 to C6 of the second group is
initiated, the switch 11 is turned off and the switch 12 is turned
on first. This operation provides switching that allocates the
ground potential (reference potential) to a signal line connected
with the positive terminal of the differential amplifier D3.
Subsequently, the switches S5 to S7 are simultaneously turned on
after the switches S1 to S3 have been simultaneously turned off,
leaving the switch S4 turned on, so that measurement of the cells
of the second group is initiated.
Because the ground potential is allocated to the positive terminal
of the differential amplifier D3 in the measurement described
above, in which the backward measurement, C4.fwdarw.D3,
C5.fwdarw.D2 and C6.fwdarw.D1, is carried out, all the differential
amplifiers D1 to D3 are able to work with a single power source. In
this way, even if a polarity of signal of a cell voltage varies
depending on a group of cells to be measured, the differential
amplifiers D1 to D3 are able to operate with a single power source,
because they work in unison in a direction of one of positive and
negative potentials with respect to a certain reference
potential.
FIG. 4 is a circuit diagram showing an example of an apparatus for
measuring voltage according to the present invention, assuming that
a group includes four cells. In a detecting circuit (voltage
detecting device) 10b shown in FIG. 4A, a PhotoMOS relay, which
withstands a total voltage of all the cells in a fuel cell, is used
for each of the switches S1 to S9 for measurement of cell voltage
and the switches S11 and S12 for switching a grounding line.
As shown in FIG. 4, measurement of cell voltage is carried out for
four cells at a time for each group. Because a common switch
(PhotoMOS relay) S5 is connected with a signal line shared by the
first and second groups, it may be possible to reduce the PhotoMOS
relays by the number comparable to that of the groups of cells in a
fuel cell in comparison with a conventional apparatus for measuring
voltage. In this case, a polarity of a signal carrying a cell
voltage, which is received by differential amplifiers D1 to D4,
reverses each time a group of cells to be measured is transferred
from one to another. More specifically speaking, a signal of cell
voltage received by the differential amplifiers D1 to D4 reverses
between positive and negative potentials each time measurement is
transferred from an oddly numbered group to an evenly numbered
group, and vice versa.
It may be necessary for the differential amplifiers D1 to D4 to
have a bipolar power supply so as to accommodate the reversal of
polarity. However, in a setup of circuit shown in FIG. 4, a first
signal line of a group of cells is connected to the ground GND by
alternately turning on one of the switches S11 and S12 each time
measurement is transferred from one group to another.
As shown in FIG. 4, the switch S11 is provided in a negative signal
line of the cell C1 of the first group so as to connect this line
to the ground GND. Similarly the switch S12 is provided in a
negative signal line of the cell C5 of the second group so as to
connect this line to the ground GND. The switches S11 and S12 are
alternately turned on and off according to an odd or evenly
numbered group: turning on the switch S11 during measurement of the
first group and turning on the switch S12 during measurement of the
second group, for example. In this way, although a polarity of a
signal of cell voltage received by the differential amplifiers D1
to D4 reverses for each switching of groups, a ground potential
(reference potential) is controlled so as to enter a reference
terminal of a differential amplifier.
Alternate switching of the ground GND using the switches S11 and
S12 as described above, which reverses a reference potential
(ground potential) of a cell voltage between negative and positive
potentials, allows use of a single power source which supplies
power to the differential amplifiers D1 to D4. In this way, the
differential amplifiers D1 to D4 do not require a bipolar power
source, but sufficiently work with a single power source.
As a result, it may be possible to double number of cells which can
be scanned at a time in comparison with an apparatus without
switching of the ground. Suppose a maximum rated voltage for a
differential amplifier is 20 volts and a cell voltage of 3 volts
for a pair of cells in this case, as shown in FIG. 1. The number of
cells which can be scanned at a time is three cells
(20V/2/3V.apprxeq.3). Because a bipolar power source is required
for the differential amplifier, the number of cells is limited to
three.
In contrast, when switching of the ground is carried out as shown
in FIG. 3, for example, and the same conditions described above are
assumed, number of cells which can be scanned at a time is six
(20V/3V.apprxeq.6). Because the number of cells turns out to be two
times that of measurement without switching the ground, it may be
possible to measure voltages of cells of a fuel cell by
higher-speed scanning.
When a signal line of the switch S5 fails due to disconnection in
case of an apparatus without switching of the ground, it may fall
into losing measurement for eight cells, the cells C1 to C4 of the
first group and the cells C5 to C8 of the second group. In
contrast, an apparatus for measuring voltage, which introduces
switching of the ground by the switches S11 and S12, may restrict
failure of measurement to only four cells, C5 to C8. As described
above, introduction of switching of the ground can decrease the
number of cells by half, which can not be measured when
disconnection of a signal line occurs.
The apparatus for measuring voltage according to the present
invention described above, which reverses a polarity of voltage of
a cell according to a group to be measured, allows shared use of a
switch, thereby contributing to a reduction in the number of parts.
In addition, because a constant polarity of cell voltage can be
detected by switching a signal line, which is connected to the
ground GND, when a polarity of cell voltage reverses, it is
possible to carry out measurement of voltage using a single power
source. This allows use of a differential amplifier, which can
operate with a single power source, thereby resulting in a
significant reduction in material cost of a detecting circuit. The
apparatus, which alternately connects one of first and last signal
lines of cells to the ground each time a polarity of a group of
cells to be measured reverses, it may be possible to double the
number of cells which can be scanned at a time in comparison with
an apparatus without switching of the ground. As a result, the
apparatus according to the present invention, which enables
high-speed scanning of multi channels, is able to provide
measurement of voltages of a group of cells, for example a fuel
cell in which a large number of cells are connected to each other
in series.
Although description has been given of the embodiment in which
measurement of cell voltage is carried out while scanning is
carried out for the cells of a fuel cell, the present invention is
not limited to the fuel cell. It may be alternatively possible to
apply the present invention not only to measurement of voltage of
cells connected to each other in series in any type of secondary
battery, but also to measurement of individual dry batteries
connected to each other in series.
Because the apparatus for measuring voltage according to the
present invention is able to detect electromotive forces of
elements in a plurality of cells connected to each other in series,
cells in a fuel cell for example, using smaller number of parts in
comparison with a conventional apparatus, it may be possible to
apply the apparatus according to the present invention to fields
where monitoring of various types of batteries is required,
especially an industrial field in which fuel cell systems are
introduced.
Foreign priority documents, JP 2004-346959 filed on Nov. 30, 2004
and JP 2004-347874 filed on Nov. 30, 2004, are hereby incorporated
by reference.
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